Recommendations for storage on GPD Win

So I've already run out of space on my Win. I'm considering buying a 128gb Samsung Fit, but 128gb isn't that much in the long run, at least for me (I might buy a few of them and switch between them as needed).

I've also been considering getting a full-sized USB stick with more capacity, or even a portable HDD or SSD, which will likely be faster and a better deal, but kind of kills the overall portability (still more portable than a laptop, though). My wallet is already drained from the Win itself, so I would prefer spending as little as possible.

So what do you guys think? What storage solution do you use for your GPD Win? Would you recommend something other than a Samsung Fit, like an external hard drive?

TL;DR What does everyone use for their Win, and what do you recommend for me if I want more than 128gb, but don't want to spend too much and want something relatively portable?